Allorecognition and graft-versus-host disease.

The development of graft-versus-host disease (GVHD) after allogeneic bone marrow transplantation (BMT) is mediated by alloreactive donor T lymphocytes infused with the bone marrow (BM) inoculum. Over the past few years, knowledge about the molecular basis of antigen (Ag) recognition, tolerance induction and activation of alloreactive T lymphocytes has increased remarkably. Recent observations also challenged the traditional view of the role and significance of various alloreactive T cell subsets and their particular effector cell functions involved in the generation of GVHD. New information which emerged from these studies has a major impact in understanding the immunobiology of GVHD. It also has important practical consequences, such as the successful prediction of GVHD before allogeneic BMT by the measurement of recipient-specific alloreactivity. The current concepts of the molecular basis of allorecognition, tolerance induction and T cell activation could be important in developing strategies to avoid GVHD while preserving a graft-versus-leukemia response.